Vacuum tube mixing circuits



Uct. 2, 3951 COLEMAN 2,569,924

VACUUM TUBE MIXING CIRCUITS Filed Oct. 30, 1948 (a g r FLIIIIIIIII 7 9/ (gsiu s'fjl 0 Est- 7! fly 8 1% 29 inwf fl 84 f f a M: 4 mm [a ,2 LZQQJ 6 T ll m Mill 6b INVENTOR Jolmflolemazz BYQK ATTORNEY Patented Oct. 2, 1951 vacuum TUBE MIXING omcurrs John H. Coleman, Princeton, N. J., asslgnor to Radio Corporation of America, a corporation of Delaware Application October 30, 1948, Serial No. 57,461

Claims. 1

This invention relates generally to vacuum tube mixing circuits and more particularly to such mixing circuits in which the cathode of the tube is cold and has deposited thereon a radioactive material and in which the space between the tube electrodes is subjected to a magnetic field.

It is known that certain isotopes are radioactive and emit nuclear charged particles at known rates over known periods of time and over a range of energy values or levels expressed in electron volts. Some emissions consist of positively charged or alpha particles, others of negatively charged or beta particles and others of both alpha and beta particles. With the emission of a charged particle from the nucleus of an atom, there occurs a transmutation of the atom into an atom of another element and this atom may or may not be radioactive and it may or may not be gaseous in form.

It is also known that when certain materials are subjected to nuclear radiation bombardment, a number of electrons around the nucleus of the bombarded atom are knocked out of their orbits and projected into space. This phenomenon is known as secondary emission. The number of secondary electrons emitted per bombarding particle depends upon the bombarded material itself and upon angle of incidence and the velocity of the bombarding particle, In general, the less the angle of incidence of a high energy particle the less is the number of secondary emitted electrons and the less the velocity of a bombarding particle, the greater is the number of secondary emitted electrons.

These secondary emitted electrons have relatively low energy values compared with the primary emission values. Their further movements after leaving the bombarded surface depends upon their initial velocities and their initial random direction and upon the electric and electromagnetic fields in the region where they leave the bombarded surface.

When these secondary electrons. strike other secondary-emission responsive materials, further secondary emissions may occur, the amount of such secondary emission depending upon the velocity of the electrons and the angles of incidence and the character of the material bombarded.

In considering the available radioactive materials, phosphorus has been selected to illustrate the invention as it is a pure beta emitter of suflicient average energy levels for the particles to reach the secondary emission responsive electrode of the tube and with sufiicient energy as to cause secondary electron emission. Also, phosphorus becomes stable after emission and is particularly adapted to high vacuum or rarified gas tube use as its decay products are not gaseous. There are, however, a large number of other suitable radioactive substances that may be used within the scope of the invention.

The instant invention comprises an improvement on the methods and systems disclosed and claimed in copending U. S. application Serial No. 51,756 filed September 29, 1948, which basic invention contemplates the use of a source of radioactive material (deposited on the cathode) and an electrode (anode) that is secondary emission responsive to the charged particle radiation of the source, the space between the source and the electrode being under vacuum and also subjected to a magnetic field proportional in strength to and corresponding in characteristics with a potential source desired to be amplified. The amplified potentials are made available in a load circuit connected between the anode anu the cathode. The basic invention also disclosed and claims the combination of the tube and associated circuits adaptable as an oscillator.

The improvement of the instant invention comprises the new modification of the basic invention of impressing on the anode and cathode, potentials originating in an independent oscillating current source, whereby the tube functions as a mixer of the frequency of the local oscillators and the frequency of the currents creating the magnetic field, to obtain currents of an intermediate frequency.

Among the objects of the invention are to provide improved methods of and means fora mixing two currents of different frequencies to obtain currents of an intermediate frequency. f

Another object is to provide a method of and means for initiating conduction currents in a vacuum tube by particles emitted from a radioactive source and controlling these conduction currents by variations of a magnetic field generated by a current of one frequency and controlling these conduction currents by currents of another frequency to obtain currents of an intermediate frequency.

Another object of the invention is to vary the strength of a. magnetic field impressed upon a vacuum tube, which tube includes a radioactive material as its cathode, in accordance with the frequency variations of an electrical signal and utilizing the corresponding variations in the magnetic field to control the currents in the load circuit of the tube and simultaneously to impress upon the tube potentials varying at a frequency 1 9,569,994 a 7 of a local oscillator to mix the two frequencies at an intermediate frequency, as will be disclosed and obtain currents of an intermediate frein-detail hereinafter.

' quency. I When there is no magnetic fleld present in the Other objects will be apparent from the despace between the source I and anode the paths scription of the invention as hereinafter set 5 of-the primaryradiation particles from sourceI forth in, detail and from the drawings made a' are straight lines from source I to anode 5, as part hereof in which: Figure 1 a schematic shown by arrow .I I. vAs the angles ofincidence diagram of an embodiment oi the'sinvention, of the paths of theparticle's to the anode 5 are showing the tube, a means for "the impressing practically zero, the particles are captured or colon'the medium of the tube of a magnetic field 10 lected by anode 5 with little secondary electron varying in accordance with a signal frequency, emission. Thisisparticularly true'of the high ameans for impressingpotentials on the cathode energy particles from source I.

and anode of the tube varyinginaccordance with If a unidirectional magnetic field is impressed the frequency of a source of local'oscillations and on the medium of the tube and the fleld' is inmeansfor utilizing the currents'of the mixed and creased, the primary charged particles, fromv v intermediate frequency; Figure '2 is a. graph source I are deflected more and more, inversely r showing. therelation of time to instantaneous as the velocity ofindividualparticles. Some of v a values ofthe currents creatingthe magnetic field;j the particles of high 'velocitieswill continue to 2 Figureiti is a graph showing the-relation 'of the ol w p -t etastra t-@131 magnetic field in gauss to the voltage acrossthe to anode 5, but the.- -p aths of-ia tube when the tube isljust non-conductingpFig 0f the m mm Ve i y-particle 1 I v ure 4'15 agraph showingfthe relation- 0f, time-to. and th rebyiincre mn the-anglesgof n dence come I the instantaneous values of the'ipotentials-imf and thus cause substantial secondary electron.

' pressed on the cathode and anod of the tube-.by

-- the local sourceof oscillations; .Figure '5.is a anode graph'showing the. relation .oftime ,to} the instan taneou's values of the-currents:- ofgthe inter' diatefrequency; Figure 6 is a' graph showing h relation "of; timeto the-instantaneous values 0 I I I 4 transcon'ductance or the. tube;.'Figure=' 7 is thefi l between s el n d heons graph'ofa family of curves showing the relation 1 6 relatwelyilow p iestth hpathsare of the currents-in the load" circuit .of the tubeto d fl c d to a co sp dm e ate e potentials}acrossthe tube for, three intensity. valuesof the magnetic1fieldimpressedpupon the, v

medium'ofthe'tube;and-Figureflyis.aschematic35Q S' n v D l j diagram -ofjthe'device-operated" ush -pullwith Whetherthese secondary-electronsreach'source 'anotherdevice." j Similar reference characters areapplle I similar element's throughoutthe-drawings. Referring tofFi'gure-LI represer'i asourc radioactive material, s uppoltedfon,rodiiwhich'lis -thecathode-"of a tubeshown g'erierally at '3';

. that the "secondary electrons; are {cut ofi from [emission to be emitted from the. s rfa e x )The sec dary electrons. are 'em itted-' from ode 5 at relatively low velocities compared with" 'f ei-primary particles, butthey are}likewiseai fcted by the magneticjfleldgand'gthej.electric" particles are acceleratedtowardsj' source I,' as source I'is ofa. positive. potential'and anode 5 2 will depend upon theiryyelocitie'sjand-the strength. of ='t h' e magneticlfield; The Stren th of;

the magnetic field andthe .Voltage'b'etween' source I andfanode .SEmaybe-adjusted to-such values.

rea'ching" sourcei .andare defiectedfto pass by.

2 is mounted-"ma conventional manneriin tub'eg3f u c If u a e ne e' conditibns a through insulator 4.1 The: anode J5fo1msithe iivelope of the tube. j The tube 'is keptu j fuum, (a residual pressure of l' th 1 I-lg) by a conventional pu p;

municating-with exhaust-co velope I of the] tube, is 'permeabl magnetic'field createdb'y-curreii Thei magnetic field; 'biase gAliiminum ha's-been foun "to I -The anode-cathode}'orloa' circuito- I consists of theJsecondaryo primary of trahsform c, source-l3. "The s'econd'a-ryjpf the' priinary.offtransforme 'series with-eachother an of the primary-of transformer from or source 2=is;;

- "where e isthefcharge-of"particle, H is the magnetic-"field, m isthe'ma ss of theparticle, .r is the radius of thesource' I; Ris the radius of anode 5 and =v is thepotentialof source I, all in C. G. S. nits -.-.('s ee" Hull, Physics Review 1921, volume 18,

ge 35 j.

lectr'ons'jpassing 'by source I continue on. their erj IZ-Ifand $1 3 5 l'mmal no under which the'secondaryjelectronsiwill-cut of! .Whehlthis cut ofi condition' isireached, the

:ourved paths'and'strike'. anode 5 causing further Isecondary.electron emissionfroni anode 5. As the" electrons that pass-by source} I are off relatively v i lowvelo'cities; t e number of-secondaryelectrons.f 15 gmundedat flfemitted per individual electronstriking anode .5,

f henfi i pmf'i fi m d f 3 is relatively high; Thusa copious-srmply offree e OH load 1 1 t. the PQS P 'termmal fi'filectrons a'rje trapped'witmn th s acefgim d il I electric'sois rce I3, ;is:conne'ct ed'fto sourcexlg and source-ly'srjwv v g TheEprimaryfzoftransformer/III connecte'dqr, Because the-secondaryfelectronsY with -b of i 'l s i im fls bw i r-from sou'r'ce *I, andare. eflected successively no e s the t f't c until, afterseveral -reflections from received signals at one freque flow th rou'ghithe'iprimarylp I another frequency, tubeisfunctionsi'asamixer tube 'and flcurrentsflow throughjitran's'former I2 diu'm and ionization of the medium-occurs.

,0 engthens .l i paths. become jlong'er fthanthejniean free path. mlgfor-jcollisi'on 'withv the] residual }m'olecules' :o'f the When thefmediumfisl ionized there; .will also 1 f f' thepositively}.charged jidns towar :Athc an de. .afasjano' e 5 is r; a-negat'ive potential. .fl-hebombardment of anode 5 by these ions will cause further secondary emission from anode I. Thus large conduction ,currents flow across the tube and through the load circuit as long as source I is positive with respect to anode 5.

It has been found by observations that when the magnetic field is reversed in direction, the same phenomenon exists. With a reversed magnetic held, the paths of the particles are deflected in the opposite direction but to the same degree for corresponding values of field strength.

In applying the invention to a practical operating condition. the constants of circuits and sources of electrical energy, such as the resistances of coils, the magnetic field produced by difierent coils under different current conditions. available voltages, etc. are known or may be determined by conventional methods.

The operating characteristics of the tube for aw range of operating conditions may likewise be determined in the same manner as for any conventional tube, that is, a series of observations are made for the various values of the variables over the desired ranges and the results of these observations are plotted as the characteristic curves of the tube. These curves are then available for selecting any desired particular operating condition.

The cut-01f characteristics of the device, that is, the conditions of operating values at which the device becomes conductive, is determined by observing the values in the elements of the circuit (Figure 1) such as the maximum strength of the magnetic field (H) in gauss required for the several values of the voltage across the tube, Va, at which the anode current is just zero, that is. when the tube is just conducting or just not conducting. A typical plot of a set of related values is shown in Figure 3, where H is the value of the magnetic field in gauss for corresponding values of Va, the anode voltage in volts, the anode current being zero, that is, the tube being just non-conductive. The non-conductive region (I) and the conducting region (II), see Figure 3, and hence the cut-oil characteristics, are thereby determined.

Likewise, the magnetic field may be successively held constant (H0, H1. and H2, respectively) and the anode current (is) observed for values of anode voltage, Va. The results of such a test are shown in Figure 7.

It will be noted in Figure 7 and in Figure 2 that the cut-01f voltage V is the minimum anode voltage at which there is no conduction currents for any value of magnetic field H.

To analyze what takes place when currents alternating at an angular velocity, as, are impressed on solenoid I and currents alternating at an angular velocity, we, the instantaneous values oi the current through solenoid 8 (is sin w: t Figure 2, and the instantaneous values 01' the voltage across the tube (eo sin wot), Figure 4, are plotted coaxi'ally with Figure 3, that is, the horizontal origin-line of Figure 3 is drawn as an extension of the horizontal origin-line of Figure2 and the vertical origin-line of Figure 4 is drawn as an extension of the vertical origin-line of Figure 3. In the figures, wo=ws.

It will be noted that the ordinates in Figure 3 are proportional to the ordinates in Figure 2 and the abscissa in Figure 3 are proportional to the abscissa in Figure 4. It is. therefore, possible to find by cross plotting the instantaneous values of the resulting alternating currents and hence the angular velocity of their alternations or their frequency. These latter values are plotted in Figure 5, the maximum points on the plotted values forming the envelope of the mtermediate frequency currents.

Another approach to the explanation of the reactions taking place in the circuit at various instants of time is by a mathematical analysis of the device.

As the conduction currents are varied in accordance with the magnetic field, the transconductance (en) may be defined as ga=6i/6H and is sketched in Figure 6 for the three time sequences oi wot=7lm-/2, where n equals 1, 5 and 9, the conductance being zero when source i is nega-- tive, that is, when n equals 2, 4 etc. The currentvoltage characteristic curves for three magnetic fields are sketched in Figure 7, as previously explained.

A general mathematical expression for the output current can be obtained'by:

=gueo sin (wt-+0) 2) where either gn or 0 can be considered time dependent and represented by the usual Fourier series over the proper limits:

gH=6an COS n Nut and , 0=sqn cos met (4) Thus, on considering a time variation in an and neglecting the phase factor, the following equation is obtained:

i=c sin w rm, cos no;

=A e sin w t-+ 0)... (nw.+w )t The Fourier coefllcients are then determined byea,. sin (nan-w n 0 a -2 g cos nwJfiwJ-l-g iti l g cos nwdtwJ (7) where m 0=sin" 0 V being the low voltage cut-oi! The conversion transconductance, represented in the usual manner by:

can be seen in the first approximation from Fig.- ure 6b.- For this particular case a r m; (max) 1 yo r (average) This value of transconductance approaches the The- '7 ventional circuits which match the stated characteristics for frequency mixing or conversion. For example, a push-pull arrangement can be used as shown in Figure 8.

Referring t Figure 8, the mediums in tube 30 and in tube 3b are subjected to a magnetic field varying in accordance with the frequency of the currents from source I. The voltages produced along the secondary of transformer I are im-- pressed upon source la and source lb. When source la is positive and tube 3a is conductive, source lb is negative and tube 3b is non-conductive, and vice versa. The anodes 5a and 5b are connected together and grounded at H). The primary of transformer I2 is connected in series with the secondary of transformer II and forms the load circuit of'the two tubes.

The reactions in the tubes and circuits are the same as previously disclosed in connection with Figure 1. It is immaterial whether solenoids 8a and 8b are connected in series or in parallel as the direction of the magnetic field along the central axis of the tubes is not critical. As previously explained, the cut-off of secondary electrons reaching the cathode (source I) occurs at the same value of the electromagnetic field, the

paths of electrons being deflected either to one side or the other but in either case missing the source lat the same value of strength of the electromagnetic. field.

There is thus disclosed a mixing circuit in which the medium in a tube (or tubes) having a radioactive source as a cathode and a secondary electron emission responsive anode, is subjected to a magnetic field varying in accordance with the frequency characteristics of one source of currents, the anode-cathode potentials are varied in accordance with the frequency characteristics of'a second source of currents and currents of an intermediate frequency are made available in the load circuit of the tube, which circuit consists of three elements: the secondary of a transformer the primary of which is connected to the said second source of currents, the primary of a transformer the secondary of which is the output of the intermediate frequency currents and a sourcev of biasing electric source, these three elementsbeing connectedin series with each other and connected as a unit between the anode and said material electric alternating potentials corresponding in frequency to that of the other of said two currents, and collecting the currents of said intermediate frequency'from a circuit associated with said source and said material.

2. The method of mixing two currents of difierentfrequencies to produce currentsof an intermediate frequency comprising: providing a source of nuclear charged particle radiation in a a l rarified gaseous medium, positioning in said'medium and adjacent said source a secondary elec-' tron emission responsive materiaL-Jimpressing upon said medium an alternating magnetic field corresponding in frequency to that of one of said two currents. impressing upon said source and said material electric alternating potentials corresponding in frequency to that of the other of said two currents, the said potentials on said source and said material being 180 degrees out of phase with each other, and collecting the currents of said intermediate frequency from a circuit associated with said source and said material.

3. The method of mixing two currents of different alternating frequencies to produce currentsof an intermediate frequency comprising: providing a rarifled gaseous-medium high vacuum tube having as its cathode a source of nuclear charged particle radiation and as its anode a secondary electron emission responsive material and having a load circuit therebetween, impressing upon said medium an alternating magnetic field corresponding in frequency to that of one of said two currents, impressing upon said anode and said cathode through said load circuit electric potentials corresponding in frequency to that of the other of said two currents, and collecting the currents of said intermediate frequency through said load circuit.

4. The method of mixing two currents of different frequencies to produce currents of an intermediate frequency comprising; providing a pair of sources of charged particle radiation 'in two separate rarified gaseous mediums, positioning in each of said mediums a secondary adjacent said electron responsive material sources, impressing upon said mediums an alternating magnetic field corresponding infrequency to that of one of said two currents, maintaining the said materials at the same potential, impressing upon said sources alternating electric potentials corresponding in frequency to that of the other of said two currents, whereby con- 40 duction currents are. generated within said tubes at a frequency intermediate the said two frequencies, and collecting the said conduction currents.

5. The method of mixing two currents of difi ggferent' frequencies to produce currents of an intermediate frequency comprising: providing a pair of sources of charged particle radiation in two separate ratified gaseous mediums, positioning in each of said mediums a secondary electron responsive material adjacent said sources, impressing upon saidmediums an alternating magnetic field corresponding in' frequency to that of one of said two currents, maintaining the said materials at the same potential, impressing upon said sources alternat-- ing electric potentials corresponding in frequency to that of the other of said two currents, the said potentials on said sources being 180 degrees out of phase with each other, whereby conduction currents are generated within said tubes at a frequency intermediate the said two frequencies, and collecting the said conduction currents. I

6. Apparatus for mixing two currents of dif- 1 ferent frequencies to produce currentsof an intermediate frequency comprising: a rarified gaseous-medium tube, a source of' nuclear charged particle radiation within said tube, a secondary electron emission responsive. material withinsaidtube and adjacent said source, means for impressing upon said medium a magnetic field alternating in accordance with the fre-' quency of one of said two currents, means for .impressing upon said source and said material electric potentials alternating in accordance; with the frequency of the other of said two currents, whereby conduction currents are generated within said tube corresponding to predetermined modulation products of said diflerent frequencies, and means for collecting the said conduction currents.

7. Apparatus for mixing two currents of different frequencies to produce currents of an intermediate frequency comprising: a rarified gaseous-medium tube, a source of nuclear char ed particle radiation within said tube, a secondary electron emission responsive material within said tube and adiacent said source, means for impressing upon said medium a magnetic field alternating in accordance with the frequency of one of said two currents, means for impressing upon said source and said material electric potentials alternating in accordance with the frequency of the other of said two currents, the said potentials on said source and said material being 180 degrees out of phase with each other, whereby conduction currents are generated within said tube corresponding to frequency intermediate said different frequencies and means for collecting the said conduction currents.

8. Apparatus for mixing currents from two sources of di ferent frequencies to produce c 'rrents of an intermediate frequency comprising: a rarified gaseous medium tube, a source of nuclear charged particle radiation within said tube, a secondary electron emission responsive material within said tube and adjacent said source, a solenoid surrounding said medium and connected to one of the said two current sources, a first transformer th primary of which is connected to the other of said two current sources, a second transformer the primary of which and the secondary of said first transformer being connected in series with each other and between said nuclear source and said material, the terminals of the secondary of said second transformer being terminals of said intermediate frequency currents.

9. Apparatus for mixing two currents of different frequencies to produce currents of an intermediate frequency comprising: a pair of rarified gaseous medium tubes, each of said tubes hav- The following references are 10 A ing therein a source of nuclear charged particle radiation and a secondary electron emission responsive material adjacent thereto, means for impressing upon said mediums a magnetic field alternating at a frequency corresponding to that of one of said two currents, means for impressing upon the said sources of said tubes electric potentials alternating at a frequency corresponding to that of the other of said two currents, means for connecting together the said materials of said tubes, whereby conduction currents are generated within said tubes corresponding to a frequency intermediate said different frequencies, and means for collecting said conduction currents.

10. Apparatus for mixing two currents of different frequencies to produce currents of an intermediate frequency comprising: a pair of rarified gaseous-medium tubes, each of said tubes having therein a source of nuclear charged particle radiation and a secondary electron emission responsive material adjacent thereto, means for impressing upon said mediums a magnetic field alternating at a frequency corresponding to that of one of said two currents, means for impressing upon the said sources of said tubes electric potentials alternating at a frequency corresponding to that of the other of 'said two currents, the said potentials on said sources being degrees out of phase with each other, means for connecting together the said materials of said tubes, whereby conduction currents are generated within said tubes corresponding to a. frequency intermediate said different frequencies and means for collecting said conduction currents.

J OHN H. COLEMZAN.

REFERENCES CITED of record in the file of this patent:

UNITED STATES PATENTS Number Name a Date 2,121,737 Hansell June 21, 1938 2,220,161 Linder Nov. 5, 1940 

